Present-day society is becoming increasingly dependent upon data communication systems. In the event of the failure of such a system, workers and facilities frequently stand idle for considerable periods of time. Rapid restoration of service is thus a matter of considerable economic significance. Determining which particular component or circuit element of the system has failed is typically done by an expert skilled in the design and operation of one or more circuit elements of the system, and is frequently much more time-consuming and error-prone than is desirable. In practice, the difficulty of prompt diagnosis of system faults is compounded by the fact that the circuit elements comprising most data communication systems are supplied by different manufacturers and vendors. If the wrong vendor is mistakenly called on to provide repair service, the actual restoration of service may be delayed by hours or days. As data communication systems have become increasingly complex, a systems analyst becomes less and less able to rapidly and accurately diagnose the cause of a system failure.